Methods and systems of determining physical characteristics associated with objects tagged with rfid tags

ABSTRACT

Methods and systems of determining physical characteristics associated with objects tagged with Radio Frequency Identification (RFID) tags. At least some of the illustrative embodiments are methods comprising making a first reading of a RFID tag coupled to an object (an electromagnetic signal received from the RFID tag having a first received signal strength indication (RSSI)), making a second reading of the RFID tag (an electromagnetic signal received from the RFID tag having a second RSSI), and a determining whether the object is moving using (at least in part) the first and second RSSI. Other illustrative embodiments, may determine (in addition to or in place of determining movement) orientation of the object based, at least in part, on the electromagnetic signals.

BACKGROUND

1. Field

The various embodiments are directed to determining motion and/ororientation objects tagged with radio frequency identification (RFID)tags.

2. Description of the Related Art

Radio frequency identification (RFID) tags are used in a variety ofapplications, such as goods identification in wholesale and retailsales, access cards (e.g., building access, garage access), and badgingand identification of employees. However, most RFID systems constrainthe RFID tags to be stationary, or only slowly moving, such that readingor interrogating of RFID tags is not adversely affected by movement ofthe RFID tags. In situations where tagged objects move quickly, specialequipment is needed to read the RFID tags. Moreover, existing systemsare typically concerned with reading RFID tags and in some casesdetermining location, but system and methods to determine whether theRFID tag is moving and/or orientation of the RFID tag (or the object towhich the tag attaches) are not commonly employed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various embodiments, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a system in accordance with at least some embodiments;

FIG. 2 shows a dual-sided patch antenna in accordance with at least someembodiments;

FIGS. 3A and 3B show far-field radiation (or reception) patterns for theantenna elements of the dual-sided patch antenna consideredindividually;

FIG. 4 shows far-field radiation (or reception) pattern for thedual-sided patch antenna of various embodiments;

FIG. 5 shows an electrical block diagram of circuitry for coupling tothe dual-sided patch antenna in accordance with at least someembodiments;

FIG. 6 shows an electrical block diagram of circuitry for coupling tothe dual-sided antenna in other embodiments;

FIG. 7 shows an electrical block diagram of circuitry for coupling tothe dual-sided antenna in yet still other embodiments;

FIG. 8 shows a system in accordance with other embodiments;

FIG. 9 shows an electrical block diagram of circuitry for coupling tomultiple reading antennas;

FIG. 10 shows an electrical block diagram of circuitry for coupling tomultiple reading antennas;

FIG. 11 shows a method in accordance with at least some embodiments; and

FIG. 12 shows a method in accordance with at least some embodiments.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, design and manufacturing companies may refer to a componentby different names. This document does not intend to distinguish betweencomponents that differ in name but not function.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . . ” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection or through anindirect connection via other intermediate devices and connections.Moreover, the term “system” means “one or more components” combinedtogether. Thus, a system can comprise an “entire system,” “subsystems”within the system, a radio frequency identification (RFID) tag, a RFIDreader, or any other device comprising one or more components. Further,various embodiments are directed to determining which side of an objectfaces a particular direction. Even though cylindrical and sphericalobjects may not have precisely defined “side” boundaries, for purposesof this specification and the claims cylindrical and spherical objectsnonetheless are considered to have sides (e.g., a first hemisphere of aspherical object is a first side, and a second hemisphere of thespherical object is a second side).

DETAILED DESCRIPTION

The various embodiments disclosed herein are discussed in the context ofradio frequency identification (RFID) tags; however, the systems andmethods discussed have application beyond RFID tags to other types ofradio frequency technologies. The discussion of any embodiment inrelation to RFID tags is meant only to be illustrative of thatembodiment, and not intended to intimate that the scope of thedisclosure, including the claims, is limited to that embodiment.

The various embodiments are directed to determining physicalcharacteristics associated with objects tagged with radio frequencyidentification (RFID) tags. FIG. 1 shows a system 100 in accordance withsome embodiments. In particular, system 100 shows an object 10 on aconveyor system 12, with the object 10 selectively moving in thedirection indicated by arrow 14. Conveyor system 12 is merelyillustrative of any situation where an object 10 moves in two- orthree-dimensional space. For example, the object 10 and conveyor system12 are illustrative of wafer boats in semiconductor manufacturingproduction line, luggage in an automated luggage handling system,parcels in an automated sorting facility, or participants in a war game.The object 10 has an associated RFID tag 16, which as illustrated isvisible both from in front of the object 10, and from behind the object10. The system 100 further comprises a reading antenna 18, which asillustrated is positioned downstream of the direction of travel of theobject 10. The reading antenna 18 is shown as a Yagi antenna, but otherantenna types (e.g. dipole, loop or patch antennas) may be equivalentlyused.

In accordance with some embodiments, a RFID reader 19 and electronicsystem 21 couple to the reading antenna 18. The RFID reader 19 may beequivalently referred as an interrogator. The RFID reader 19 passes dataobtained from the RFID tag 16 to the electronic system 21, whichperforms any suitable function. For example, the electronic system 21,based on the data received from the RFID tag 16, may identify the nextstep in a semiconductor manufacturing processes, direct a piece ofluggage down a particular conveyor, direct a parcel to a particularshipping container, or identify participants in a war game. Inaccordance with some embodiments, the RFID reader 19 and/or theelectronic system 21 (which may be a computer system) determine whetherthe object 10 is moving using, at least in part, a received signalstrength indication (RSSI). Thus, the discussion turns to a descriptionof RSSI.

In active and semi-active RFID tags, once queried by the RFID reader,the RFID tag broadcasts an electromagnetic signal using power from abattery internal to the RFID tag. The electromagnetic signal has encodedtherein an identification value pre-programmed in the RFID circuit ofthe RFID tag. Stated otherwise, the electromagnetic signal carries amessage, and the identification value is encoded in the data payload ofthe message, possibly along with other information and values. Theelectromagnetic signal is received by the reading antenna 18, and theRFID reader 19 extracts the message from the electromagnetic signal.When the active and/or semi-active RFID tag is very close to the readingantenna 18, the signal strength of the electromagnetic signal is high.Conversely, when the active and/or semi-active RFID tag is far from thereading antenna 18 (e.g. at a far edge of an operational zone), thesignal strength of the electromagnetic signal may be low, and yet theRFID reader may still be able to extract the message and correspondingvalue of interest. In accordance with at least some embodiments, theRFID reader 19, in addition to extracting the message from theelectromagnetic signal, also generates and/or calculates a parameterindicative of the signal strength of the electromagnetic signal thatcarried the message, the RSSI. For example, when the active and/orsemi-active RFID tag is very close to the reading antenna, the RSSI maybe a maximum (e.g., a RSSI value of 100), and when the active and/orsemi-active RFID tag is at the far reaches of the usable range, the RSSImay be a minimum (e.g., a RSSI value of 1).

Passive RFID tags, unlike active and semi-active RFID tags, have nointernal battery. The antenna of the passive RFID tag receives aninterrogating signal transmitted from a reader circuit and attachedantenna, and the power extracted from the received interrogating signalis used to power the tag. Once powered, the passive RFID tag sends aresponse comprising a data or identification value; however, the valueis sent in the form of backscattered electromagnetic signals to the RFIDreader 19 antenna 18. In particular, the RFID reader 19 and antenna 18continue to transmit power after the RFID tag is awake. While the RFIDreader 19 transmits, an antenna of the RFID tag is selectively tuned andde-tuned with respect to the carrier frequency. When tuned, significantincident power is absorbed by the antenna of the RFID tag 16 (and isused to power the underlying circuits). When de-tuned, significant poweris reflected by the antenna of the RFID tag 16 to the antenna 18 of theRFID reader 19. The data or identification value thus modulates thecarrier in the form of reflected or backscattered electromagnetic wave.The RFID reader 19 reads the data or identification value from thebackscattered electromagnetic waves. Thus, in this specification and inthe claims, the terms transmitting and transmission include not onlysending from an antenna using internally sourced power, but also sendingin the form of backscattered signals.

In reading of passive tags, a RSSI value may also be calculated. Whenthe passive RFID tag is very close to the reading antenna 18, thedifference in backscattered signal strength as between when the antennaof the RFID tag is absorbing power, and when the RFID tag is reflectingpower, may be very high. Conversely, when the passive RFID tag is farfrom the reading antenna 18, the difference in backscattered signalstrength as between when the antenna of the RFID tag is absorbing powerand when the RFID tag is reflecting power may be very low, and yet thereader circuit may still be able to extract the message andcorresponding value of interest. Here too, the RFID reader 19, inaddition to extracting the message from the electromagnetic signal, alsogenerates a parameter (RSSI) indicative of the signal strength of theelectromagnetic signal that carried the message. In the case of RSSI forpassive tags, the RSSI may be an indication of the ratio of the peakreflected signal strength (i.e., RFID tag reflecting power) to thebackground signal strength (i.e., RFID tag absorbing power). In otherembodiments, the RSSI for passive tags may be the ratio of a maximumpossible reflected power (i.e., signal strength with RFID tag close tothe reading antenna and the RFID tag reflection) to the actual reflectedpower. As an example of possible RSSI, when the passive RFID tag is veryclose to the reading antenna, the RSSI may be a maximum (e.g. a RSSIvalue of 100), and when the RFID tag is at the far reaches of the usablerange, the RSSI may be a minimum (e.g., a RSSI value of 1).

Regardless of the active or passive construction of the RFID tag used,in accordance with some embodiments a determination is made as towhether the RFID tag 16 and attached object 10 are moving by evaluatingRSSI for multiple readings or interrogations of the RFID tag. Forembodiments where the electronic system 21 (as opposed to the RFIDreader 19) makes the determination of whether the object 10 is moving,the RFID reader 19 passes the identification value derived from theinterrogation of the RFID tag 16 along with the RSSI for the particularinterrogation to the electronic system 21, and the electronic system 21compares RSSI values to make the determination. In other embodiments,the RFID reader 19 is configured to retain identification values andRSSI from previous interrogations. Using retained RSSI, the RFID reader19 makes the determination of whether the object is moving and passes anindication of the movement, or lack of movement, to the electronicsystem 21. Independent of the precise location where the determinationis made, in some embodiments movement is determined as a difference inRSSI values for different interrogations of the RFID tag 16. Forexample, if a first interrogation yields a RSSI of 50, and a subsequent(though not necessarily immediately subsequent) interrogation yields aRSSI of 75, the difference in the RSSI as between the two interrogationsis indicative of movement of the RFID tag 16 and thus the underlyingtagged object 10.

Further embodiments determine not only whether the object is moving, butalso direction of movement. Consider the example above of a firstinterrogation resulting in a RSSI of 50, and a subsequent interrogationresulting in a RSSI of 75. As the RFID tag 16 moves closer to thereading antenna 18, the RSSI increases, and given that the subsequentreading has a higher RSSI, the RFID reader 19 and/or the electronicsystem 21 deduce that the RFID tag 16 and attached object 10 are movingtoward the reading antenna 18. Now consider the opposite situation,where a first interrogation yields a RSSI of 75, and a subsequentinterrogation yields a RSSI of 50. As the RFID tag 16 moves away fromthe reading antenna 18, the RSSI decreases, and given that thesubsequent reading has a lower RSSI, the RFID reader 19 and/orelectronic system 21 deduce that the RFID tag 16 and attached object 10are moving away from the reading antenna 18. Stated otherwise,increasing RSSI as between two interrogations indicates movement towardthe reading antenna 18, while decreasing RSSI as between twointerrogations indicates movement away from the reading antenna 18.

Many atmospheric conditions affect electromagnetic signal propagation(e.g. dust and other suspended particles, and to a lesser extentrelative humidity), and thus a user implementing embodiments illustratedby FIG. 1 may desire confirmation as to movement and/or direction ofmovement. In such situations, a second reading antenna 20 may bepositioned within the system and, as illustrated, the reading antenna 20is positioned upstream of the expected path of travel of the RFID tag 16and attached object 10. As shown, the reading antenna 20 may have adedicated RFID reader 23, and in other embodiments the reading antennas18 and 20 share a RFID reader, with the reader multiplexing between thetwo (or more) antennas. In embodiments using multiple reading antennas,each reading antenna is used to make a plurality of interrogations ofthe RFID tag 16. While analysis of calculated RSSI of the plurality ofinterrogations from one reading antenna may show movement toward thereading antenna, analysis of RSSI associated with the plurality ofinterrogations from the second reading antenna may confirm the movement.The confirmation may be either by recognizing movement away from thesecond reading antenna (where the second reading antenna is upstream ofthe expected path of travel) or by recognizing movement toward thesecond reading antenna (when the first and second reading antennas aresubstantially co-located). If the movement determination associated withthe second reading antenna is contradictory to the determination of thefirst reading antenna (e.g. both antennas show movement toward therespective antenna when the antennas are upstream and downstreamrespectively), then the movement determination for both antennas may beignored, or the contradictory determinations may signal the need forcalibration and or maintenance.

The embodiments discussed to this point are operational with RFID tagshaving any of a variety tag antennas. For example, RFID tag 16 maycomprise a dipole antenna, a loop antenna or a single-sided patchantenna. In the case of a single-sided patch antenna, assuming the patchantenna faces the reading antenna 18, reading antenna 20 may not be ableto interrogate the RFID tag 16. In some embodiments, object 10 may befitted with a RFID tag system comprising a plurality of RFID tags 16(e.g., one on the upstream face, and one on the downstream face, toaddress having both upstream and downstream reading antennas). Otherembodiments address certain shortcomings of the single-sided patchantenna by employing a dual-sided patch antenna, as illustrated in FIG.2.

FIG. 2 shows a perspective view of a dual-sided patch antenna 200 inaccordance with at least some embodiments. The dual-sided patch antenna200 comprises a first radiative patch or antenna element 30. The antennaelement 30 comprises a sheet of metallic material (e.g. copper) in theform of a square or rectangle in this example. The length and width ofthe antenna element 30 is dictated by the wavelength of the radiofrequency signal that will be driven to the antenna element 30 (or thatwill be received by the antenna element 30), for example driven by wayof lead 32. More particularly, the length and width of the antennaelement 18 are each an integer ratio of the wavelength of the signal tobe transmitted (or received). For example, the length and width may beapproximately half the wavelength (λ/2) or a quarter of the wavelength(λ/4).

The dual-sided patch antenna 200 also comprises a ground plane or groundelement 34. The antenna element 30 and the ground element 34 each definea plane, and those planes are substantially parallel in at least someembodiments. In FIG. 2, the ground element 34 length and width and theantenna element 30 length and width are shown to be approximately thesame; however, the ground element length and width may be larger orsmaller in other embodiments. Although the antenna element 30 and groundelement 34 may be separated by air, in some embodiments a dielectricmaterial 36 (e.g. printed circuit board material, silicon, plastic)separates the antenna element 30 from the ground element 34.

Still referring to FIG. 2, the dual-sided patch antenna 200 furthercomprises a second radiative patch or antenna element 38. Much likeantenna element 30, the antenna element 38 comprises a sheet of metallicmaterial (e.g. copper) in the form of a square or rectangle in thisexample. The antenna element 38 defines a plane, and in some embodimentsthe plane defined by antenna element 34 is substantially parallel to theplane defined by ground element 34. The length and width of the antennaelement 38 is dictated by the wavelength of the radio frequency signalthat will be driven to the antenna element 38, for example driven by wayof lead 36, and in some embodiments the length and width as between theantenna elements 30 and 38 are the same. Although the antenna element 38may be separated from the ground element 34 by air, in other embodimentsa dielectric material 40 (e.g. printed circuit board material, silicon,plastic) separates the antenna element 38 from the ground element 34.Each antenna element 30, 38 comprises a centroid axis 42 (i.e., centroidbeing the point considered to be the center), and in some embodimentsthe centroid axis 42 of each antenna element are substantially coaxial.

Radio frequency signals are driven to each of the antenna elements 30and 38 by way of probe feeds or feed points (i.e., the locations wherethe radio frequency signals couple to the antenna elements), such asfeed point 44 for antenna element 30 (the feed point for antenna element38 not visible in FIG. 2). The feed points are coupled to theirrespective leads 32 (for feed point 44) and 36 (for the feed point ofthe antenna element 38). The following discussion is directed to antennaelement 30 and feed point 44, but the discussion is equally applicableto antenna element 38. As illustrated, the feed point 44 resides within(internal of) an area defined by the length and width of the antenna,and the internal location of the feed point is selected based on severalcriteria. One such criterion is the impedance seen by a radio frequencysource that drives the antenna element 30. For example, shifting thefeed point toward the center of the antenna element 30 along its length(“L” in the figure) tends to lower the impedance seen by the radiofrequency source, while shifting along the length towards an edge (e.g.,edge 46) tends to increase impedance seen by the radio frequency source.Moreover, the placement of the feed point 44 also controls polarity ofthe electromagnetic wave or signal created. For example, the feed point44 as shown creates an electromagnetic signal whose electric fieldpolarization is substantially along the length L. Shifting the feedpoint toward a corner (e.g., corner 48), or also using a second feedpoint centered along the length L, creates a circularly polarizedelectromagnetic wave. Thus, the feed points are internal to the lengthand width to meet these, and possibly other, design criteria. Thediscussion now turns to directivity of the dual-sided patch antenna.

Consider for purposes of explanation that the centroid axis 42 liesalong the 0°-180° axis in an overhead view (i.e., looking down on thelength L from above) of the dual-sided antenna of FIG. 2, and thatantenna element 30 faces the 180° direction while antenna element 38faces the 0° direction. FIGS. 3A and 3B illustrate a far-field radiationpattern for each of the antenna elements 30 and 38 respectively. Inparticular, FIG. 3A shows that antenna element 30 considered alone has afar-field radiation pattern that is substantially directed along thecentroid axis away from the ground element 34. The plot of FIG. 3A isvalid for both overhead and elevational (i.e., looking horizontallytoward the width W) plots of far field radiation. Likewise, antennaelement 38 considered alone has a far-field radiation pattern that issubstantially directed along the centroid axis away ground element 34,and the plot (of FIG. 3B) is equally valid for both overhead andelevational plots of far-field radiation. Considering the far-fieldradiation patterns of antenna element 18 and antenna element 24together, the dual-sided patch antenna 200 has a quasi-omnidirectionalradiation (or reception) pattern, as illustrated in FIG. 4, with FIG. 4equally valid for both overhead and elevational plots of far-fieldradiation. Stated otherwise, the far-field radiation pattern for thedual-sided patch antenna is substantially the same in all three spatialdirections.

The far-field radiation patterns of FIGS. 3A, 3B and 4 show directivity,but one or more parameters of the physical system may affect theultimate far-field radiation pattern. For example, ground elementslarger than the antenna elements 30, 38 increase the size of the dips50A and 50B at the 90° and 270° orientations, while a ground element thesame size or slightly smaller may make the radiation pattern morecircular (as indicated by dashed lines 52A and 52B). The far-fieldradiation patterns of FIGS. 3A, 3B and 4 also show gain (in decibels(dB)), but no specific numbers except that the gain may be greater than0 dB in all directions. The actual gain values are related to parametersof the physical system such as frequency of operation and the dielectricstrength of the dielectric material 36 and 40.

FIG. 5 illustrates an electrical block diagram of RFID tag 16 (of FIG.1), where the RFID tag 16 comprises a dual-sided patch antenna 200. Inparticular, in the embodiments of FIG. 5 the antenna elements 30 and 38are coupled to a matching or tuning circuit 54. The purpose of thetuning circuit is to tune the two coupled antennas to be resonant at aparticular frequency or set of frequencies. The tuning circuit, in turn,is coupled to an RFID circuit 56. The tuning circuit 54 and RFID circuit56 may comprise an integrated product, such as the MCRF42X family ofproducts available from Mirochip Technologies, Inc. of Chandler, Ariz.The RFID circuit 56 holds the identification value or values, and isresponsible for transmitting the value to the reader (i.e., throughbroadcasting using power from in internal battery, or by backscatterusing power from the interrogating signal).

FIG. 6 shows an electrical block diagram of other embodiments where thetwo antenna elements of the dual-sided patch antenna 200 areelectrically isolated from each other by way of isolation circuits. Inparticular, antenna 30 is coupled to tuning circuit 58, which in turncouples to an additional isolation circuit 60 and RFID circuit 56. Inthese embodiments, the isolation circuit 60 may comprise one or more ofa power supply (PS) 62 and additional buffer 64. Likewise, antenna 38 iscoupled to tuning circuit 66, which in turn couples to isolation circuit68 and RFID circuit 56. Further in these embodiments, the isolationcircuit 68 may comprise one or more of a power supply (PS) 70 and buffer72. Operation of the power supply and buffer is discussed with respectto antenna 30, but the discussion is equally applicable to antenna 38.When antenna 30 is not exposed to an interrogating signal from a RFIDreader (e.g. RFID reader 19 of FIG. 1), the buffer 64 electricallyisolates (or de-couples) the antenna element 30 from the RFID circuit56. However, when exposed to an interrogating signal, the buffer 64couples the antenna 30 to the RFID circuit 56. In active tags, a batterymay be the power supply 62 to provide power to sense electromagneticsignals received by the antenna element 30, and to control theadditional buffer 64. Because the power supply 70 may be self powered,the location of the power supply 70 and the buffer 72 may be reversed.Moreover, a rectifying circuit may be present either in the power supply70 or buffer 72 to convert incoming data and commands to baseband data.Using battery power, the buffer 64 continuously or periodicallydetermines if antenna element 30 is receiving an interrogating signal.If so, the buffer 64 couples the antenna element 30 the RFID circuit 56(e.g., by biasing the gate of a transistor to allow coupling of at leasta portion of the interrogating signal to the RFID circuit 56), withpower to run the buffer provided from the battery.

In semi-active and passive tags, the power supply 62 rectifies receivedpower from the interrogating signal, converts the received power todirect current (DC) (e.g. using Schottky diodes), and uses at least someof the converted power to control the buffer 64. For example, the buffer64 may be configured to electrically isolate the antenna element 30 fromthe RFID circuit 56 when no power is provided from the power supply 62(i.e., when there is no interrogating signal received by the antennaelement, or where the interrogating signal is of insufficient strengthto power the buffer 64). When an interrogating signal is incident uponthe antenna element 30, the power supply 62 extracts power from thesignal, and uses the power to drive the buffer and couple the antennaelement 30 to the RFID circuit 56. Thus, regardless of the tag type,when an interrogating signal is received on antenna element 30, thesignal is coupled to the RFID circuit 56, which responds to the reader19 (FIG. 1) with an identification value.

FIG. 7 illustrates yet still further alternative embodiments of a RFIDtag 16. In particular, in the embodiments illustrated in FIG. 7 eachantenna element 30, 38 of the dual-sided patch antenna 200 couples toits own tuning circuit and RFID circuit. Antenna element 30 couples totuning circuit 74 and RFID circuit 76, while antenna element 38 couplesto tuning circuit 78 and RFID circuit 80. RFID circuits 70 and 74 may bedesigned and configured to hold and provide the same identificationvalues when interrogated, or different values. Thus, when interrogatedthe RFID circuits 76 and 78 may respond with the same value, or withdifferent values. Further, the two RFID circuits may be coupled in orderto share data or to enable other functionality.

Returning to FIG. 1, with RFID tag 16 having a dual-sided patch antenna200 with one antenna element facing or exposed to the reading antenna18, and the other antenna element facing or exposed to the readingantenna 20, then embodiments discussed above where movement anddirection of movement are verified by reading antenna 20 may be used.Additionally, using RFID tag 16 with dual-sided patch antennas enablesdetermination of more than just movement and direction of movement.

Consider situations where the RFID tag 16 of FIG. 1 has a dual-sidedpatch antenna 200, with each antenna element having a dedicated RFIDcircuit pre-programmed with different identification values (i.e., FIG.7 with RFID circuits 76 and 80 having different identification values).In the illustrative situation of FIG. 1 with the assumptions ofdifferent identification values, when reading antenna 18 is used tointerrogate the RFID tag 16, a particular value is determined. Whenreading antenna 20 is used to interrogate the RFID tag 16, a differentidentification value is determined. Thus, if a first identificationvalue is associated with a first side 82 of the RFID tag 16 (and thusthe first side 84 of the object 10), obtaining the first identificationvalue by interrogation of the RFID tag 16 with the reading antenna 18reveals an orientation of the RFID tag 16 and attached object 10 (i.e.,which direction the RFID tag 16 and attached object 10 are facing).Likewise, if a second identification value is associated with a secondside 86 of the RFID tag 16 (and thus the second side 88 of the object10), obtaining the second identification value by interrogation of theRFID tag 16 with the reading antenna 20 reveals an orientation of theRFID tag 16 and attached object 10 (i.e., again, which direction theRFID tag 16 and attached object 10 are facing). The system 100 may thusdetermine an orientation, in these embodiments the orientation beingwhich side of the RFID tag 16 and attached object 10 face or are exposedto a particular direction. Moreover, combined with the variousembodiments using RSSI to determine whether the RFID tag 16 and attachedobject 10 are moving (and in some cases which direction), the system 100may thus determine which face of the object is exposed to the particularreading antenna, and in which direction the face is moving.

Detecting orientation by determining which side of the RFID tag 16 andattached object 10 face a particular direction are not limited toembodiments having RFID tags 16 with dual-sided patch antennas 200 anddedicated RFID circuits for each antenna element. Consider a situationwhere the RFID tag 16 of FIG. 1 has a dual-sided patch antenna 200, butonly a single RFID circuit shared between the two antenna elements(i.e., embodiments of FIG. 5 or 6). While the identification valuereceived from the RFID tag 16 will be the same regardless or independentof which antenna elements is interrogated (because of the shared RFIDcircuit), the antenna elements of the dual-sided patch antenna 200 maybe configured with different physical characteristics to distinguish thetwo antenna elements.

FIG. 8 illustrates a system 800 in accordance with further embodimentsthat distinguish the two antenna elements based on characteristics ofthe electromagnetic signal transmitted by each antenna element. Inparticular, system 800 shows object 10 on the illustrative conveyorsystem 12, with the object 10 selectively moving in the directionindicated by arrow 14. The object 10 has an associated RFID tag 16comprising a dual-sided antenna 200 (only one antenna element 90 isvisible). The system 900 further comprises reading antennas 92, in thisexample comprising two patch antennas 94 and 96. The reading antennas 92are shown positioned upstream of the direction of travel of the object10 such that the feed points of the respective patch antennas arevisible in the drawing, but the patch antennas may be alternativepositioned downstream of the path of travel, or there may be readingantennas both upstream and downstream of the path of travel. Electronicsystem 21 and RFID reader 19 couple to the reading antennas 92, and theRFID reader 19 reads the RFID tag 16 by way of an antenna element of theRFID tag 16 positioned so as to be exposed to the reading antennas 92(in the illustrative situation of FIG. 8, the antenna element of theRFID tag 16 that is exposed to the reading antennas 92 is not visible).

In accordance with these embodiments, the reading antennas 92 areconfigured to preferentially receive electromagnetic signals ofdifferent polarizations. For example, because of the location of thefeed point 98 for patch antenna 94, the patch antenna 94 preferentiallyreceives electromagnetic signals having vertically oriented electricfield components. Stated otherwise, patch antenna 94 is said to havevertical polarization. Because of the location of the feed point 99 forpatch antenna 96, the patch antenna 96 preferentially receiveselectromagnetic signals having horizontally oriented electric fieldcomponents. Stated otherwise, patch antenna 96 is said to havehorizontal polarization. While the illustrative reading antennas 92 areshown as patch antennas, any set of antennas having differentpolarizations (even if the difference in polarization is by way ofidentical antennas in different physical orientations) may be used. IfRFID tag 16 responds to an interrogation from the RFID reader 19 with avertically oriented electromagnetic signal, patch antenna 94 will have ahigh RSSI for the response, while patch antenna 96 will not receive theresponse, or will receive are response with a low RSSI. Conversely, ifRFID 16 responds to an interrogation from the RFID reader 19 with ahorizontally oriented electromagnetic signal, patch antenna 96 will havea high RSSI for the response, while patch antenna 94 will not receivethe response, or will receive a response with a low RSSI.

In these embodiments, in order to determine which face of the RFID tag16 is exposed to the reading antennas 34, each antenna element of thedual-sided patch antenna 200 is configured to have differentpolarizations. In the illustration of FIG. 8, antenna element 90 of thedual-sided patch antenna 200 is shown to have a feed point 102configured for transmitting electromagnetic signals with verticalelectric field polarization. Though not visible, in accordance withthese embodiments the antenna element of dual-sided patch antenna 200that is exposed to the reading antennas 92 is configured fortransmitting electromagnetic signals with horizontal electric fieldpolarization. Thus, in spite of the fact that each antenna element ofthe dual-sided patch antenna 200 in these embodiments responds with thesame identification value, the RFID reader 19 and/or electronic system21 may determine which face of the RFID tag is exposed to the readingantennas 92 by the polarization of the response to the interrogatingsignal (so long as the object 10 is constrained to a particularrotational orientation). Moreover, in addition to determiningorientation being which face of the RFID tag 16 is exposed to thereading antennas, the RFID reader 19 and/or electronic system 21 maymake determinations as to whether there is movement of the RFID tag 16and attached object 10, and if there is movement detected, the directionof movement may be determined based on RSSI values of a plurality ofreadings of the RFID tag 16.

The embodiments with respect to determining an orientation based on thepolarization of electromagnetic signals are discussed as having verticaland horizontal electromagnetic signals and related antennas; however,any two different polarizations may be used. For example, one face(first antenna element) of the RFID tag 16 could be identified by aright circularly polarized electromagnetic signal, and the second face(second antenna element) of the RFID tag 16 could be identified by aleft circularly polarized signal. Further still, one face of the RFIDtag 16 could be identified with a circularly polarized electromagneticsignal (right or left), and the second face could be identified by avertical (or horizontal) polarized electromagnetic signal.

Consider now a situation such as FIG. 8 where the RFID tag 16 usesdual-sided patch antenna 200, with each antenna element having adedicated RFID circuit (as shown in FIG. 7), and further with eachantenna element having different polarizations. In these embodiments,not only does the RFID reader 19 and/or electronic system 21 distinguishwhich face of the RFID tag 16 is exposed to the reading antennas 92, butalso determines the rotational orientation of the RFID tag 16 andattached object 10. In particular, because each antenna element of thedual-sided patch antenna 200 has a dedicated RFID circuit, programmingeach RFID circuit with separate identification values means that theRFID reader 19 and/or electronic system 21 is capable of deducing whichface of the RFID tag 16 is exposed to the antenna system 92. If antennaelement 90 of the dual-sided patch antenna 200 is configured to havevertical polarization when the object 10 is vertically oriented, and thesecond antenna element of the dual-sided patch antenna 200 is configuredto have horizontal polarization when the object 10 to his verticallyoriented, then the polarization of the electromagnetic signal receivedat the reading antennas is indicative of the rotational orientation ofthe RFID tag 16 and object 10.

With the illustrative orientation and polarizations in mind, if the RFIDreader 19 receives an identification value indicating antenna element 90is exposed to the reading antennas 92, and moreover that the receivedelectromagnetic signal was vertically polarized, then the face of theRFID tag 16 comprising antenna element 90 is exposed to the readingantennas 94, and the RFID tag 16 and object 10 are vertically oriented.Similarly, if the RFID reader 19 receives an identification valueindicating antenna element 90 is exposed to the reading antennas, andmoreover that the received electromagnetic signal was horizontallypolarized, then the face of the RFID tag 16 comprising antenna element90 is exposed to the reading antennas 92, but the RFID tag 16 and object10 are horizontally oriented (i.e., rotated 90° about an axis defined byline 14). A similar situation exists for the antenna element of RFID tag16 that is not visible in FIG. 8; nevertheless, the RFID reader 19and/or the electronic system 21 may determine that the particular faceof the RFID tag 16 comprising the antenna element is exposed to thereading antennas (based on the identification values), and a rotationalorientation of the RFID tag 16 and object 10 (based on the polarizationof the electromagnetic signals).

Embodiments that determine which face of the RFID tag 16 is exposed tothe reading antennas (based on the identification values) and theorientation of the RFID tag 16 and attached object 10 (based on thepolarization of the electromagnetic signal) may also determine movementof the RFID tag 16 and attached object 10 (as discussed above usingdifferences in RSSI as between a plurality of interrogations), and alsodirection of movement (again as discussed above using the rising orfalling difference in RSSI as between a plurality of interrogations).

Still referring to FIG. 8, yet still other embodiments determinephysical characteristics being orientation and/or movement, but notnecessarily which face of the RFID tag 16 is exposed to the readingantennas. Consider a situation where the RFID tag 16 delivers the sameidentification value regardless of the antenna element exposed to thereading antennas (i.e., shared RFID circuit as in FIGS. 5 and 6, orseparate RFID circuits programmed with the same identification value asin FIG. 8), and also that each reading antenna element has the samepolarization (e.g. vertical polarization). The reading antennas 92, RFIDreader 19 and/or electronic system 21 may thus determine rotationalorientation based on the polarization of the electromagnetic signalreceived. In the specific case of vertically polarized antenna elementswhen the object 10 is vertically oriented, a received electromagneticsignal with a vertical orientation (i.e., received by patch antenna 94)indicates the object 10 is vertically oriented. Likewise, a receivedelectromagnetic signal with a horizontal orientation (i.e., received bypatch antenna 96) indicates the object 10 is horizontally oriented.Moreover, the RFID reader 19 and/or electronic system 21 may determinemovement of the movement of the RFID tag 16 and attached object 10 (asdiscussed above using differences in RSSI as between a plurality ofinterrogations), and also direction of movement (again as discussedabove using the rising or falling difference in RSSI as between aplurality of interrogations).

The embodiments discussed with respect to FIGS. 1 and 8 show multiplereading antennas (i.e., reading antennas 18 and 20 for FIG. 1, andreading antennas 92 for FIG. 8 comprising patch antennas 94 and 96).FIG. 9 illustrates at least some embodiments of coupling the readingantennas to underlying RFID reader. In particular, FIG. 9 shows tworeading antennas 104A and 104B (which antennas could be, for example,antennas 18 and 20 respectively of FIG. 1, or patch antennas 94 and 96respectively of FIG. 9). The reading antennas 104A and 104B in FIG. 9couple to a single RFID reader 19 by way of multiplexer 106, and theRFID reader 19 also couples to an electronic system 21. FIG. 10illustrates yet still further embodiments, where reading antennas 104Aand 104B couple to reader circuits 19A and 19B respectively, and eachreader circuit 19A and 19B then couples to electronic system 21.

The various embodiments where the face of the RFID tag 16 exposed to thereaders is determined were discussed in relation to a dual-sided patchantenna 200 with each element having a RFID circuit, or a dual-sidedpatch antenna 200 having a single RFID circuit but with differentpolarizations of the antenna elements; however, in other embodimentsRFID tags with a dual-sided patch antenna may be replaced with multipleRFID tags coupled on each face of the object. For example, each face ofthe object may have an RFID tag, but each RFID tag provides a differentidentification number when interrogated. Thus, the face of the objectmay be determined based on the identification number. As yet anotherexample, each face of the object may have a RFID tag where each RFID tagprovides the same identification number when interrogated, but thepolarization of the electromagnetic signals is different for each RFIDtag. In this example, the face of the object may be determined based onthe polarization of the received signal.

In a related manner, the various embodiments of determining therotational orientation of the RFID tag and/or attached object werediscussed in relation to a dual-sided patch antenna 200 with eachantenna element having specific polarization; however, in otherembodiments RFID tags with dual-sided patch antennas may be replacedwith multiple RFID tags coupled on each face of the object. For example,each face of the object may have an RFID tag, with the polarization ofthe antenna for the each RFID tag related to a particular orientation ofthe object. Thus, by determining the orientation of the electromagneticsignal at the reading antenna, the orientation of the object can bedetermined.

FIG. 11 shows a method in accordance with at least some embodiments. Inparticular, the method starts (block 1100) and moves to receiving afirst electromagnetic signal from a radio frequency identification(RFID) tag coupled to an object (block 1104). Next, a first RSSI iscalculated based on the first electromagnetic signal (block 1108). Themethod also comprises receiving a second electromagnetic signal from theRFID tag (block 1112) and calculating a second RSSI based on the secondelectromagnetic signal (block 1116). Finally, a determination is made asto whether the object is moving using, at least in part, the first andsecond RSSI (block 1120), and the illustrative method ends (block 1124).In some embodiments, determining whether the object is moving may alsocomprise determining whether the object is moving toward or away from areading antenna, with the determining based, at least in part on thefirst and second RSSI. For example, if the first RSSI is a relativelylow number and the second RSSI is a relatively high number, then it maybe deduced that the RFID tag is moving toward the reading antenna.Conversely, if the first RSSI is a relatively high number and the secondRSSI is a relatively low number, then it may be deduced that the RFIDtag is moving away from the reading antenna.

FIG. 12 illustrates other methods in accordance with the variousembodiments. In particular, the method starts (block 1200), and moves tosending an interrogating signal to the RFID tag coupled to an object(block 1204). Based on the interrogation the RFID tag sends anelectromagnetic signal, and thus the next step in the illustrativemethod may be receiving an electromagnetic signal transmitted by a RFIDtag (block 1208). Thereafter, a determination is made as to theorientation of the object, with the determination being based, at leastin part, on the electromagnetic signal (block 1212), and the method ends(block 1216). Determining the orientation may take many forms. In someembodiments determining the orientation further comprises determiningwhich side of the object substantially faces a reading antenna. In yetfurther embodiments, determining orientation further comprisesdetermining a rotational orientation of the object.

The dual-sided patch antenna 200 of FIG. 2 may be constructed in severalways. In some embodiments, the antenna 200 may be constructed usingflexible sheets of metallic and dielectric material adhered together andcut to appropriate dimensions. In alternative embodiments, the antenna200 may be manufactured, such as by deposition of the metallic portionsand growth of dielectric portions by way of semiconductor manufacturingtechniques. In yet still other embodiments, the antenna 200 may beconstructed using a combination of techniques, such as depositingmetallic layers on a dielectric material such as a printed circuit board(PCB), and then mechanically coupling two or more PCBs to form theantenna.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. For example, while the antenna200 is shown with a single ground element, the dual-sided patch antenna200 may be manufactured by adhering two patch antennas back-to-back,meaning that two ground elements may be present, yet same advantagesachieved. It is intended that the following claims be interpreted toembrace all such variations and modifications.

1. A method comprising: receiving a first electromagnetic signal from aradio frequency identification (RFID) tag coupled to an object;calculating a first received signal strength indication (RSSI) based onthe first electromagnetic signal; receiving a second electromagneticsignal from the RFID tag; calculating a second RSSI based on the secondelectromagnetic signal; and determining whether the object is movingusing, at least in part, the first and second RSSI.
 2. The method asdefined in claim 1 wherein determining whether the object is movingfurther comprises determining whether the object is moving toward oraway from a reading antenna, the determining based, at least in part, onthe first and second RSSI.
 3. The method as defined in claim 1 whereinreceiving the first and second electromagnetic signals further comprisereceiving from the RFID tag having an antenna being one or more selectedfrom the group consisting of: a dipole antenna; a loop antenna; a patchantenna; and a dual-sided patch antenna.
 4. The method as defined inclaim 1 further comprises determining orientation of the RFID tag. 5.The method as defined in claim 4 wherein determining orientation furthercomprises determining which side of the RFID tag substantially faces areading antenna.
 6. The method as defined in claim 5 wherein determiningwhich side of the RFID tag substantially faces the reading antennafurther comprises one or more selected from the group consisting of:receiving a value from the RFID tag that indicates which side of theRFID tag faces the reading antenna; and receiving the electromagneticsignal with a particular polarization, the polarization indicates whichside of the RFID tag faces the reading antenna.
 7. The method as definedin claim 4 wherein determining orientation further comprises determiningwhich of a plurality of RFID tags substantially faces a reading antenna.8. The method as defined in claim 7 wherein determining which of aplurality of RFID tags substantially faces a reading antenna furthercomprises one or more selected from the group consisting of: receivingan identification value that indicates which of the plurality ofidentification tags faces the reading antenna; and receiving theelectromagnetic signal with a particular polarization, the polarizationindicates which of the plurality of RFID tags faces the reading antenna.9. The method as defined in claim 4 wherein determining orientationfurther comprises determining rotational orientation of the RFID tag.10. The method as defined in claim 9 wherein determining rotationalorientation of the RFID tag further comprises receiving theelectromagnetic signal with a particular polarization, the polarizationindicative of the rotational orientation of the RFID tag.
 11. A systemcomprising: a frequency identification (RFID) tag configured to coupleto an object; a reading antenna in operational relationship to the RFIDtag; and a reader circuit coupled to the reading antenna, the readercircuit configured to generate a received signal strength indication(RSSI) for each interrogation of the RFID tag; wherein the system isconfigured to determine whether the RFID tag is moving based on RSSI asbetween two interrogations of the RFID tag.
 12. The system as defined inclaim 11 wherein the reader circuit is configured to determine whetherthe RFID tag is moving.
 13. The system as defined in claim 11 furthercomprising an electronic system coupled to the reader circuit, whereinthe electronic system is configured to determine whether the RFID tag ismoving.
 14. The system as defined in claim 11 wherein the system isconfigured to determine a direction of movement of the RFID tag.
 15. Thesystem as defined in claim 14 wherein the system is configured todetermine whether the RFID tag is moving toward or away from the readingantenna based, at least in part, on RSSI as between two interrogations.16. The system as defined in claim 11 further comprising: wherein theRFID tag has two faces; and wherein the system is configured todetermine which face of the RFID tag is exposed to the reading antenna.17. The system as defined in claim 16 further comprising: wherein theRFID tag further comprises a dual-sided patch antenna, each particularpatch of the dual-sided patch antenna transmits an electromagneticsignal when the particular patch is interrogated; wherein the system isconfigured to determine which face of the RFID tag is exposed to thereading antenna based on the electromagnetic signal.
 18. The system asdefined in claim 17 wherein the system is configured to determine whichface of the RFID tag is exposed to the reading antenna based on datapayload encoded in the electromagnetic signal.
 19. The system as definedin claim 17 wherein the system configured to determine which face of theRFID tag is exposed to the reading antenna based on the polarization ofthe electromagnetic signal.
 20. The system as defined in claim 19further comprising: wherein the reading antenna comprises: a firstantenna having a first polarization; and a second antenna having asecond polarization different than the first polarization; wherein thesystem is configured to determine polarization of the electromagneticsignals based, at least in part, on which of the first or secondantennas have greater RSSI for the electromagnetic signal.
 21. Thesystem as defined in claim 11 further comprising: wherein the RFID tagcouples to a first side of the object; and a second RFID tag couples toa second side of the object; wherein the system is configured todetermine which side of the object faces a reading antenna.
 22. Thesystem as defined in claim 21 further comprising: wherein the RFID taghas a first identification value; wherein the second RFID tag has asecond identification value different than the first identificationvalue; and wherein the system is configured to determine which RFID tagfaces a reading antenna based on which of the first or secondidentification values are received from an interrogation.
 23. The systemas defined in claim 21 further comprising: wherein the RFID tag has atag antenna with a first polarization; wherein the second RFID tag has atag antenna with a second polarization different than the firstpolarization; and wherein the system is configured to determine whichRFID tag faces a reading antenna based on polarization of anelectromagnetic signal received by the reading antenna.
 24. The systemas defined in claim 11 wherein the system is configured to determinerotational orientation of the RFID tag.
 25. The system as defined inclaim 24 wherein the system is configured to determine rotationalorientation of the RFID tag based on the polarization of theelectromagnetic signal.
 26. The system as defined in claim 25 furthercomprising: wherein the reading antenna further comprises: a firstantenna having a first polarization; and a second antenna having asecond polarization different than the first polarization; wherein thesystem is configured to determine rotational orientation of the RFID tagbased, at least in part, on portions of the electromagnetic signalreceived by each of the first and second receiving antennas.